HYDROGEN IN PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITION INSULATING FILMS

There exists a strong interdependence between deposition conditions, thin film composition (especially hydrogen concentration) and thin film parameters in the case of plasma-enhanced chemical vapour deposition (PECVD) silicon nitrides deposited in quartz tube reactors in the kilohertz frequency range. Besides deposition temperature and total pressure, the composition of the reacting gas mixture exerts a significant influence on the hydrogen concentration of PECVD SiN. Low partial pressures of hydrogen do not necessarily lead to low hydrogen concentrations in the layers. The combined influence of N:Si ratio and hydrogen content may lead to contrary changes of technologically relevant parameters as seen in the case of SiN(N2) and SiN(NH3) according to the etch rate in HF solutions. Hydrogen concentrations above 30 at.% lead to a hardening effect of PECVD SiN surfaces. The same effect can be obtained by phosphorus doping of PECVD silicon nitrides and especially oxynitrides, whereas PECVD oxides tend to become softer with increasing phosphorus doping. Hydrogen diffusion coefficients in PECVD SiN and SiO were derived from hydrogen concentration profiles in these layers. Hydrogen effusion during thermal stress can be a reason for remarkable changes and severe degradation of technologically relevant parameters of PECVD thin films. Therefore in this work emphasis was laid on the reasons, mechanisms and effects of incorporation and movement of hydrogen in PECVD SiN thin films.